Boron phosphide, BP, is a wide band gap AIIIBV semiconductor compound with a diamond-like structure.
It is refractory and is characterized by high thermal and chemical stability (up to 1500 K in air), remarkable thermal conductivity and very high hardness (HV of about 30 GPa) well-above that of tungsten carbide (between 18 and 22 GPa) or silicon carbide (25 GPa), the most prominent materials used in the industry of very hard materials.
In spite of these outstanding properties, boron phosphide has met with limited use to date because of the lack of a relatively simple and economical method for its production. As a result, boron phosphide is not commercially available at an industrial scale.
Boron phosphide has been synthesized by direct interaction of the elements or by reaction between halogenides of boron and phosphorus in the presence of sodium. Boron phosphide single crystals may be grown by the crystallization from flux solutions or by gas-transport reactions in two-zone furnaces.
WO 03/065465 and EP1564820 disclose a process for depositing boron phosphide on semiconductors. The method used is the atmospheric pressure metal organic chemical vapor deposition (MOCVD) using a starting material system of triethylborane/phosphine/hydrogen ((C2H5)3B/PH3/H2) at a temperature comprised between 950 and 1100° C.
GB 931,336 discloses several processes for the preparation of boron phosphide starting from metallic phosphorus or an alloy thereof and metallic boron, a boron alloy or boron carbide at a temperature corresponding at least to the sintering temperature of boron phosphide.
U.S. Pat. No. 3,260,571 discloses the preparation of boron phosphides wherein the ratio B/P is comprised between 6:1 and 100:1. These boron phosphides are prepared by reacting metallic phosphorus and boron, by reacting phosphorus halogenides and boron halogenides, by reacting boron and phosphine or from phosphates and borates in a molten metal in the presence of a reducing agent such as carbon.
Ananthanaryanan et al (Synthesis of single crystal boron phosphide. Journal of crystal growth, 1973, vol. 20, pages 63-67) disclose the preparation of boron phosphide from metallic phosphorus, boron and boron oxides, a mixture of boron and phosphorus.
As illustrated by prior art, the methods employed for preparing boron phosphide to date require expensive, toxic and aggressive reagents, complicated technical implementation, high labour intensity and time consumption.
There is therefore a need for a simple, convenient and low-cost process for the preparation of boron phosphide.